Removal of foreign element from a well



Aug. 20, 1968 Y T, JR" ET AL 3,397,743

REMOVAL OF FOREIGN ELEMENT FROM A WELL Filed April 19, 1965 A TTORNE I United States Patent 3,397,743 REMOVAL OF FOREIGN ELEMENT FROM A WELL Horace B. Bryant, Jr., Houston, Tex., and Lyle T. Colfman, Glenville, W. Va., assignors to Air Reduction Company Incorporated, New York, N.Y., a corporation of New York Filed Apr. 19, 1965, Ser. No. 449,219 9 Claims. (Cl. 166-42) ABSTRACT OF THE DISCLOSURE The subject matter relates to a method and apparatus for assisting in the removal of tools which have become stuck in a well. Generally, tools become stuck due to ac cumulations of sand or other granular material which jam or block the tool and prevent proper operation or removal. By pressurizing the material in the area of the blockage with gas and then reducing the pressure, the material may be at least partly removed.

Summazy 0f the invention This invention relates to the removal of solid material in granular form from a well in the earth. The solid material to be removed is first subjected to an inert gas under pressure. The gas pressure is maintained so that the gas permeates the solid material. The gas pressure is then reduced at the well head allowing the gas to escape and carry the solid material out of the well.

This invention relates to the removal of solid material from a well in the earth, and more especially from oil wells. The invention is intended primarily for releasing stuck tools, such as swabbing tools and drilling tools.

It is an object of the invention to provide an improved method for removing sand and other granular material from the region of a tool that has become stuck in a well as the result of the presence of the sand or other material. Swabbing tools become stuck as the result of deposition of sand or other material on top of and around the cups of the tool. Sometimes the sand is fracture sand which has been pumped into the well with wellstimulation fluid, and sometimes the sand or other material is part of the producing formation itself. In the case of stuck drilling tools, the material collecting above the tools and preventing lifting of the tools, is sometimes the result of the falling away of sand or other material from the walls of the bore above the drill bit.

Another object of the invention is to provide a method for loosening and removing sand and other granular material from a region of a well by charging compressed gas into the interstices of sand and other granular material that has collected above a tool and then releasing the pressure rapidly enough to loosen the sand or other material by expansion of the gas which has permeated the interstices.

The invention can be used in wells which are filled with fluid, such as water or mud. The compressed gas is used to lift the liquid out of the well with rapid decrease of bottom hole pressure brought about by reduction in the hydrostatic head.

The invention can be used in Wells which have no liquid if well head pressure control equipment is available to permit the building up of substantial gas pressure in the well preparatory to the rapid release of pressure and resulting gas expansion and loosening of the sand or other granular material which causes a tool to stick.

Another object is to remove from an oil well drilling bits and broken drill strings, or other objects which have come loose from the cables or pipes leading into the well. Such objects, referred to as fish in the oil industry,

3,397,743 Patented Aug. 20, 1968 "ice are included in this specification within the generic term tool. Although the actual recovery operation is different when a drilling tool such as a drilling bit has become disconnected from the drilling string, as compared with a tool which is merely stuck, the procedure of this invention for loosening the tool from the formation which caused it to come loose or stuck is essentially the same.

In its broadest aspects, it is an object of the invention to provide an improved method for removing sand or other granular material from a well regardless of whether the sand or other material is at a location to cause a tool to stick or has accumulated in a Well at a location which causes a blockage of the cross section of the well.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIGURE 1 is a diagrammatic View of an oil well having a swabbing tool stuck in the well as the result of accumulation of fracture sand above the tool and around the cups of the tool;

FIGURE 2 is a diagrammatic view of an oil well in which drilling tools are stuck as the result of sand and other material falling from the walls of the well above the drilling bit; and

FIGURE 3 is a diagrammatic view of apparatus for removing sand and other granular material from a well.

FIGURE 1 shows an oil well 10 having a casing 12 with perforations 14 communicating with an earth stratum 16 where oil flow has been stimulated by producing fractures 18 in the stratum.

A swabbing tool 20 has an accumulation of fracture sand 22 above and around the swabbing tool and in suflicient quantity to cause the swabbing tool to stick in the well so that it can not be lifted by a cable 24 that connects the swabbing tool 20 with hoist apparatus 28 at the well head.

The well 10, above the tool 20 and sand 22, is filled with water 30. The well 10 is closed at the top by a cap 32 and flow of water from the well is controlled by a valve 34.

In order to remove the sand 22, a conduit or tubing string 36 is inserted into the well and is extended to bring a lower or discharge end 38, of the conduit 36, into the region of the sand 22.

Compressed gas is charged into the well through the conduit 36. In the preferred operation, the gas is pumped into the well by apparatus which will be described in connection with FIGURE 3. For the present, it is sufficient to understand that the compressed gas enters the well through the conduit 36 and builds up a gas pressure in the region of the sand 22.

Because of the hydrostatic head of the Water 30, there is a substantial pressure on the sand 22, but even if there were no water in the well, a substantial quantity of sand above the swabbing tool 20 packs tightly enough to prevent upward movement of the swabbing tool in the well.

During the first step of the operation, the compressed gas is supplied at an elevated pressure. It is advantageous to have the pressure from the conduit 36 as high as possible and maintained long enough to permit the compressed gas to permeate the interstices of the mass of sand 22. The time required for such permeation of the gas into the sand depends upon the sand formation, the density of packing, and upon the depth of the sand blockage and the density of fluid in the well. Sometimes it is not practical to remove the full depth of sand in one operation.

Theoretically, dilferent kinds of compressed gas can be used, but from a practical standpoint, nitrogen is preferred. One advantage of nitrogen is that it eliminates the 3 fire hazard that would .be present if air, or oxygen were used. Another advantage is that the nitrogen has only slight solubility in the water or oil or other liquids which 'are likely to be encountered in the Well. The-preferred method of the invention, therefore, uses nitrogen, and preferably nitrogen which is supplied to the site in a liquid condition for reasons which will be explained in connection with FIGURE 3.

After the gas permeation period, the pressure of the gas in the region of the sand 22 is rapidly released. With the well full of fluid 30, the most practical method of release is to temporarily increase the pressure in the conduit 36 to a value greater than the hydrostatic head so that the gas lifts the fluid from the well. As the fluid is lifted and discharged through the valve 34, the hydrostatic head decreases rapidly since the gas which displaces the fluid has a lower density and therefore a lower hydrostatic pressure compared to that of the fluid.

The reduction in pressure causes the gas which has permeated the sand 22 to expand and loosen the sand so that the loosened sand is blown up through the well with the upwardly flowing gas. Although the pressure reduction is necessary to expand the gas that has penetrated the sand and for the purpose of loosening the sand, it is also necessary to increaase the flow rate from the conduit 36 so that the velocity of the upward flow of gas in the well is sufficient to carry the loosened sand with it. The required velocity depends upon many factors, for example, upon the size of the sand grains.

When all of the fluid 30 has been discharged from the well 10, suflicient sand may have been removed to release the swabbing tool 20. If such is not the case, the operation is repeated and during the period when the gas is permeating the sand, it will permeate a new volume of sand which was below the sand already removed and which was protected from the gas in the first operation by the quantity of sand above it. Unless the sand is very deep and densely packed, the tool can be released in a single operation.

Although the operation in FIGURE 1 has been described as performed with sand 22, it will be understood that the expression sand is used in a broad sense to cover granular material. Heavier particle sizes require higher gas velocities but the more densely packed materials require a more rapid reduction in pressure in order to loosen the mass and to dislodge particles into the stream of rising gas. Sand, such as used for fracture sand, can usually be effectively dislodged by a pressure drop of approximately four hundred pounds per square inch per minute. More rapid pressure drops are, of course, even more eifective. This value is given merely by way of illustration.

FIGURE 2 is a diagrammatic showing of an oil well 40 in which drilling tools 42 are stuck by sand and other granular material 44 which has fallen from the walls of the well 40 in suflicient quantity to make it impossible to pull the drill bit 42 up without danger of breaking a drill string 46 by which the drill bit 42 is operated from the surface.

The drill string 46 is of conventional construction and has a conduit 48 extending through it for its full length and communicating with nozzles 50 on the drill bit 42. In conventional operations, mud or other fluid is pumped through the nozzles 50 for removing cuttings.

In order to remove the granular material 44, the same procedure can be used as in FIGURE 1. However, it is also possible to use a slightly different procedure because of the fact that there is already a conduit 48 through which gas can be introduced into the region of the well containing the stuck drill bit 42 and the material 44 which causes the drill bit to be stuck. Compressed gas from a supply line 52 is charged into the well through the conduit 48 and nozzles 50. The streams of gas are indicated in FIGURE 2 by the reference characters 56. The original supply ofgasjsat a substantial pressure sufiicient to permeate the mass of material 44 and the pressure is maintained long enough to have the gas charge the interstices of the mass of material 44.

The well in FIGURE 2 can be filledgwith water or other liquid, as in the case of FIGURE 1, but in the construction illustrated in FIGURE 2, the upperend of the well is shown 'closedby blowout 'preventer's 62 which may be rotatable. A' mud flow line 66 .le 'ads' from the wall below the blowout ,prevente rs 62 andis controlled by a valve 68. Pressure'is. built up and maintained in the Well 40 by keeping the valve 68 closed until the mass of material 44 is sufliciently permeated and charged by the compressed nitrogen supplied through the conduit 48. A

At the end of the gas permeation period, the valve 68 is opened and the expansion of gas in the mass of material 44 loosens the mass. The flow rate through the conduit 48 is immediately increased and maintained at suflicient velocity to pickup the loosened material 44 and to carry it up through the well 40 and out through the mud flow line 66.

FIGURE 3 shows a well 70 having a drill bit '72 connected with the well head by a drill pipe 74. The well 70 has a blowout preventer 76 and has a gas supply line 52 connected with the conduit that leads down through the drill pipe 74. The oil well 70 has a mud flow line 66 with control valves 68, 77 and a mud tank 80.

Acid or oil can be introduced into the drill pipe 74 through a supply line 82 which communicates with the drill pipe and which is commanded by a valve 84.

The supply of nitrogen to the well 70 preferably comes from a tank truck 86 having an insulated tank 88 in which nitrogen is transported in a liquid condition. The liquid nitrogen is pumped from the tank 88 by one or more pumps 90 driven by a motor 92 which may be the motor that drives the truck 86. The speed of the motor is regulated by a throttle 94; and by changing this speed, the rate of discharge of the pumps 90 can be changed to change the rate of fiow of 'gas to well 70.

The supply line conduit 52 is, part of the conduit through which nitrogen from the tank 88 is delivered to the region of the well 70 at which sand or other granular material is to be loosened.

The pumps 90 discharge the nitrogen, still in a liquid condition, into a heating chamber 96 on the truck 86. This chamber contains, for example, heat exchange coils 97 for promoting evaporation of the'liquidnitrogen so that the nitrogen is in a gaseous condition when it is delivered to the well 70. These coils 97 are part of the conduit through which nitrogen passes from the tank 88 to the well.

It is highly advantageous to use liquid nitrogen and to pump the nitrogen while in liquid condition. This makes it possible to obtain extremely high rates of gas flow with pumps of limited displacement. For example, one cubic foot of liquid nitrogen delivered by the pumps 90 is equal to 696 cubic feet of nitrogen gas at standard conditions. In the preferred operation of the invention, the gas is supplied to the wells 10 and 40 of. FIGURES 1 and 2, re spectively, in the same way as illustrated in FIGURE 3..

For removing sand blockage from a region of an oil well, the method is similar to that described in connection with FIGURE 1. The process operates in substantially the same way whether the mass of packed sand or other material is' located adjacent to a tool or is lodged in a particular location of a well where there is no tool.

The invention has been described in connecton with oil wells, for which it is particularly intended. The term oil wells is meant to include gas'wells and combinations of oil and gas wells. v

The preferred embodiments of the invention hav been illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

I claim:

1. The method of removing a stuck tool from a well, which method comprises introducing nitrogen gas under pressure into the region of the well where the tool is stuck, maintaining the pressure for a period of time sufiicient for the gas to penetrate the interstices of the materials above and around the tool, then releasing the pressure of the nitrogen gas quickly so that the gas that has penetrated the material expands to dislodge some or all of said material from the region of the tool, and when sufficient material has been loosened from the region of the tool to free it, removing the tool.

2. The method described in claim 1 characterized by pumping nitrogen gas under pressure into a well that is filled with liquid, continuing slow rate pumping while gas is forced into the material around and adjacent to the stuck tool, which increases the gas pressure to a value greater than the hydrostatic pressure, and then increasing the flow rate of the gas into the well to unload the space above said region to discharge the liquid and to release the hydrostatic pressure.

3. The method of removing, from a well in the earth, a stuck drill tool on the end of a drill string having a conduit therein extending from the well head of the tool and having an opening through the lower side of the tool for discharge of fluid from the conduit, which method comprises charging gas under pressure through the conduit in the drill string and from the opening into the region of the well below the tool, charging the gas into said region at a high flow rate so as to build pressure therein, maintaining said increased pressure in said region so that the gas can at least partially permeate the mass of material surrounding said tool, reducing the pressure above the tool to expand the gas, and flowing the gas upward with substantial velocity to carry out particles from around the drilling tool and to release the drilling tool from its stuck condition.

4. The method of removing solid material from a well in the earth, which method comprises charging into the well, at the region from which said material is to be removed, a volume of nitrogen gas under substantial pressure, maintaining said region under said pressure long enough to allow the gas to at least partially permeate said material, reducing the pressure and withdrawing the gas upward in the well, with resulting loosening of the solid material, introducing additional nitrogen gas at an increased flow rate at said region of reduced pressure to maintain a rapid flow of the gas upward and an upward movement of the loosened solid material, passing said nitrogen gas to said region in the well through a closed conduit so that the nitrogen gas, during its introduction into the well, is kept out of contact with any fluid in the well above said region, said nitrogen gas being pumped into the well at a high rate of flow with a pumping device of relatively small displacement by pumping the nitrogen in a liquid state and then evaporating the liquid nitrogen before it reaches said region in the well.

5. The method described in claim 4 characterized by evaporating the nitrogen after it leaves the pumping device and before it enters the Well on its way down to the region 'from which the solid material is to be removed.

6. The method described in claim 4, in a well which is filled with liquid above said region, which method is characterized by charging the nitrogen gas into said region at a pressure at least equal to that exerted by the hydro static head above the region, and continuing the charging of nitrogen gas into the well while lifting the liquid out through the top of the well with resulting reduction in pressure exerted by the hydrostatic head.

7. The method of removing solid material from a well in the earth which method comprises first passing a supply of acid to the region from which solid material is to be removed, leaving the acid in contact with the material at said region long enough 'for chemical reaction of the acid on said material, displacing the acid by introducing nitrogen gas under pressure at said region and below said acid, maintaining said region under said pressure long enough to allow the gas to at least partially permeate said material, reducing the pressure and withdrawing the gas upward in the well with resulting loosening of the solid material, introducing additional gas at an increased flow rate at said region of reduced pressure to maintain a rapid flow of the gas upward and an upward movement of the loosened solid material, said nitrogen gas being passed to said region through a closed conduit so that the nitrogen gas, during its introduction into the well, is kept out of contact with any fluid in the well above said region.

8. The method of freeing a stuck tool from a well, which method comprises introducing gas under pressure into the region of the well where the tool is stuck, said pressure being suflicient to cause said gas to permeate at least a portion of the material which is causing the tool to be stuck, rapidly releasing the gas pressure in the region of the well where the tool is stuck so that the gas in the well expands and carries at least part of said material upward.

9. The method described in claim 8 in which gas is introduced into the region of the well where the tool is stuck at an increased flow rate following the said release of gas pressure.

References Cited UNITED STATES PATENTS 1,774,640 9/1930 Dunn l6644 3,100,528 8/1963 Plummer et al 16642 3,104,707 9/ 1963 Overly l6646 3,170,517 2/1965 Graham et al. 16642 3,246,696 4/1966 Fox 166-46 2,964,109 12/1960 Martin 16643 OTHER REFERENCES Bufiington, Multi-purpose Nitrogen Provides New Drilling Too Drilling-April 1962, pp. 54-56.

Uren, Petroleum Production Engineering, Development, 4th edition, McGraw-Hill Book Co., Inc., New York, 1965-pp. 31732l.

STEPHEN J. NOVOSAD, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,397,743 August 20, 1968 Horace B. Bryant, Jr., et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 73, "hav" should read have Column 5, line 26, "of" should read to Column 6, line 8, "the" first occurrence, should read said Signed and sealed this 10th day of February 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, 1R1

Attesting Officer Commissioner of Patents 

